Preheating oil shale prior to pyrolysis thereof

ABSTRACT

Oil shale is preheated to temperatures in the order of 400*F to 650*F prior to the pyrolysis thereof in a retort to produce vaporous hydrocarbonaceous products therefrom by entraining the oil shale with hot flue gases in a series of at least two dilute phase fluidized beds having an incineration zone interposed upstream of the final fluidized bed for reheating flue gases threfrom, and for combusting oil shale fines and hydrocarbon vapors evolved during the preheating operation and entrained in the flue gases prior to discharge to the atmosphere.

United States Patent 1191 1111 3,925,190

BEST AVAILABLE COPY Whitcombe et al. Dec. 9, 1975 4] PREHEATING OILSHALE PRIOR TO 3,164,541 1/1965 Linden et al 208/11 PYROLYSIS THEREOF3,265,608 8/1966 Crawford 208/11 3,617,468 11/1971 Reyburn et a1. 208/11Inventors: J Whltmmbe, L08 Angeles, 3,803,022 4/1974 Abdul-Rahrnan208/11 Califi; Kenneth D. Van Zanten, Llttleton, (F0104 George C- Kane,Primary ExaminerDelbert E. Gantz Paclfic Pahsades, Cahf- AssistantExaminer-James W. Hellwege 7 Assignee; The o Shale Corporation, LosAttorney, Agent, or Firm-Brumbaugh, Graves,

Angeles, Calif: Donohue & Raymond [22] Filed: July 29, 1974 [57]ABSTRACT [21] PP N04 4921447 Oil shale is preheated to temperatures inthe order of 400F to 650F prior to the pyrolysis thereof in a re- [52]US. Cl 208/11; 201/12 to Produce vaporous hydrocarbonaceous Products 511111.01. C10G 1/02 therefrom by training the Shale with hot flue [58]Field of Search 208/11; gases in a Series at least two dilute Phasefluidized 201M245; 196/120 beds having an incineration zone interposedupstream of the final fluidized bed for reheating flue gases thre- 5References Cited from, and for combusting oil shale fines and hydrocar-UNITED STATES PATENTS bon vapors evolved during the preheating operationand entrained in the flue gases prior to discharge to 3,008,894 ll/l96lCulbertson 201/12 the atmosphere 3,020,209 2/1962 Culbertson et al.201/12 3,058,903 10/1962 Otis 208/11 8 Claims, 1 Drawing figurePREIIEATING OIL SHALE PRIOR TO PYROLYSIS THEREOF BACKGROUND OF THEINVENTION The pyrolysis of oil shale by solid-to-solid heat transfertechniques to convert the kerogen content of oil shale into oil andother gaseous hydrocarbons is well known as exemplified by thedisclosures in U.S. Pat. Nos. 3,265,608 and 3,691,056. In these priorart processes, oil shale is preheated and thereafter pyrolyzed bysolid-to-solid heat transfer contact with heat-carrying bodies toproduce shale oil and other effluent vapors. Upon completion of thekerogen conversion, the heat-carrying bodies are recycled through areheating zone for further use in pyrolyzing additional preheated oilshale.

In general, the process herein described is an improvement in the oilshale preheating procedure disclosed in the above-cited prior artpatents which utilizes the residual sensible heat of the flue gasespreviously employed in the process to heat the heat-carrying bodies. Inthe above-cited U.S. Pat. No. 3,265,608, the transfer of heat from thehot flue gases to the crushed shale is accomplished by entraining theshale with flue gases heated to about 1100F in a gas lift line, i.e.,dilute phase fluidized bed. The shale is thereby preheated to atemperature of about 300F. In the preheat zone, the raw shale and hotflue gases pass co-currently up the lift line during the heat transferoperation. At the top of the gas lift line, the partially cooled fluegas is separated from the shale and vented to the atmosphere at atemperature substantially higher than the temperature to which the rawshale is preheated prior to being pyrolyzed. While this preheatprocedure conserves a portion of the waste heat contained in the ballheater flue gas, it has not been completely satisfactory when utilizedto achieve higher levels of preheating, that is, above about 300F to400F. While the method of preheating shale is not described in detail inU.S. Pat. No. 3,691,056, the process herein described may be used toadvantage to obtain high levels of preheat.

It is generally known that the conversion of kerogen into shale oil andother hydrocarbonaceous vapor does not readily occur at temperaturesless than about 500F, although some of the very fine raw shale may beprematurely pyrolyzed when contacted with very hot flue gases.Additionally, oil shale usually contains some bitumen which can bepartially vaporized during the preheat operation. Because both thesesituations are likely to occur when crushed oil shade is preheated totemperatures as high as 600F prior to entering the pyrolysis zone, thesevaporized hydrocarbons may be lost to the recovery system by beingdischarged directly to the atmosphere at relatively high temperatures.Such a situation is not only economically inefficient, but it is alsoecologically undesirable.

SUMMARY OF THE INVENTION It is, therefore, a primary object of thepresent invention to provide a process for preheating crushed oil shaleprior to the retorting thereof in a pyrolysis Zone without significantlyeffecting premature pyrolysis of a majority of the oil shale prior tothe retorting operation.

A further object of the invention is to provide a process for recoveringthe heating value of oil shale fines and pyrolyzing the remainingportion of crushed oil 2 shale so as to recover substantially 100% ofthe hydrocarbons contained in the oil shale.

A still further object of the invention is to provide for combusting oilshale fines which essentially eliminates the fines as a potential sourceof hydrocarbon emissions.

Another object of the present invention is to provide a process forpreheating oil shale prior to the pyrolysis thereof which willefficiently recover a substantial portion of the heating value of thehydrocarbons generated during the preheat operation as fuel within thepreheat system and thereby minimize the emission of hydrocarbons to theatmosphere.

These and other objectives are accomplished according to the presentinvention by preheating crushed raw oil shale in a series of at leasttwo dilute phase fluidized beds,.i.e. gas lift lines or lift pipes,having an incineration zone interposed therebetween through which theflue gas from the final preheat zone is passed prior to contacting andpreheating additional oil shale to a temperature between that of theinitial raw shale temperature and the final preheat temperature prior tointroduction of the preheated shale into the pyrolysis zone. When oilshale is preheated in this manner, it is possible to heat the shale to atemperature in the range of from about 400F to about 650F withoutemitting significant amounts of hydrocarbons to the atmosphere as theresult of premature pyrolysis of the oil shale during the preheatingoperation.

The preheat procedure of this invention provides for a gradual heatingof the oil shale through the use of a series of dilute phase fluidizedbeds which are each operated at different flue gas temperatures. Dilutephase fluidized beds are used to obtain rapid heat transfer from fluegas to a solid with a fairly wide range of particle size distribution.Because of this range of particle size, the finer particles are heatedmuch more rapidly than the larger particles. For this reason, it isimportant to control the flue gas temperature at the inlet to the liftline to minimize premature pyrolysis and hydrocarbon generation. It hasbeen found that the major portion of the hydrocarbons evolved during thepreheat operation occurs when the shale (Green River Formation) isheated to temperatures in excess of 350F. At temperatures below 350F,hydrocarbon concentrations in the flue gas discharged to the atmosphere,resulting primarily from partial vaporization of the bitumen content ofthe shale, have been shown to be less than ppm. At preheat temperaturesin the order of 500F to 600F, hydrocarbon concentrations in the flue gasare generally in the order of 500 to 1000 ppm. These higherconcentrations are caused by partial pyrolysis of the kerogen inaddition to vaporization of the bitumen. From an environmentalstandpoint, the emission of excessive amounts of hydrocarbons isundesirable. However, if the generation of large amounts of hydrocarbonscan be effectively controlled and the heat content thereof utilized, itis advantageous in terms of both conserving the natural resource andimproving project economics by generating limited amounts for use as aprocess fuel. Tests, which are described in greater detail below,indicate that as much as 5 to 15% of heat required to preheat oil shalefrom ambient temperature to about 550F can be supplied by the oil shalefines and hydrocarbons evolved during the preheat operation.

Accordingly, this process provides for a gradual preheating of the wholeoil shale to a temperature of about 350F without the generation ofsignificant concentrations of hydrocarbons, the further preheating ofthe whole oil shale to between 400F and 650F with the attendantgeneration of hydrocarbons, and the recovery of the heating value ofthese evolved hydrocarbons as well as the heating value of oil shalefines which are entrained in the flue gas. The preheat procedures ofthis invention utilize the final stage of dilute phase fluidized bedpreheating to generate hydrocarbons and entrain these hydrocarbons,together with the oil shale fines, in the flue gas stream which is thenpassed to an incineration zone wherein the heating value of thesematerials is recovered. It has been found that the evolved hydrocarbonsand the entrained oil shale fines can be efficiently burned attemperatures between about 1300F and 1500F. Higher temperatures could beutilized if increased levels of carbonate decomposition can betolerated. It has also been found that virtually complete incinerationcan be accomplished in about 0.3 second to 1.0 second at thesetemperatures. The hot flue gas from the incineration zone is partiallycooled by conventional heat recovery techniques and is used to preheatcooler raw shale in upstream (shale side) preheat stages. Thetemperature of the flue gas which contacts the oil shale in the upstreampreheat stages must be low enough, usually less than about 800F to 900F,to avoid generating and discharging significant amounts of hydrocarbonsto the atmosphere.

Two stages of preheat with one intermediate flue gas incineration andreheating operation adequately accomplish the objectives discussedabove; however, three stages of preheat utilizing a single flue gasincineration zone located between the second and third stages arepreferred. Two interstage incineration zones may also be advantageouslyutilized wherein one incineration zone is located between the first andsecond preheat zones and the other incineration zone is located betweenthe second and third preheat zones.

DESCRIPTION OF THE PROCESS Oil shale crushed to nominal /2-inch size isfed from the crusher and introduced into a first dilute phase fluidizedbed preheat zone wherein the shale is contacted with flue gas at atemperature sufficient to partially preheat the shale and remove thefree moisture. The flue gas discharged from this first stage is passedto the atmosphere after passing through a dust removal apparatus, suchas a bag filter, electrostatic precipitator, web scrubber, or the like.In the higher temperature preheat zones located downstream of the firstpreheat zone, the oil shale is heated to increasingly highertemperatures by contacting the shale with hotter flue gases from theheat-carrying body reheating zone. The preheated oil shale from thefinal preheat zone is passed to the pyrolysis zone. The partially cooledflue gases from the preheat zones located downstream (gas side) of thefinal preheat zone are passed through one or more interstageincineration zones wherein the flue gases are reheated by incinerating amixture of fuel, entrained hydrocarbons and raw shale fines.

Temperature control of the flue gases fed to the various preheat zonesmay be accomplished by blending additional cool, fresh air or flue gaswith the primary hot flue gas stream or by passing the flue gasesthrough heat exchangers.

DESCRIPTION OF THE PREFERRED EMBODIMENT The process hereinafterdescribed in connection with the accompanying drawing utilizes acombination of three dilute phase fluidized bed preheat zones with oneinterstage incineration zone located between the second and third(final) preheat zones to preheat oil shale from about 50F to atemperature of about 500F to 600F prior to the pyrolysis thereof. Thedrawing is a process flow diagram of the preferred embodiment of theinvention described in combination with the pyrolysis process describedin the above-cited US. Pat. No. 3,265,608. The following Table 1 presenta typical With reference to the embodiment as illustrated in thedrawing, freshly crushed oil shale (including fines and moisture) iscontinuously charged at about 50F to lift line or first preheat zone 10at a rate of about 450 tons per hour wherein it is contacted andtransported with relatively warm flue gas at about 475F fed from line11. The flue gas to the first preheat zone 10 from line 11 is a blend ofthe flue gas having a temperature of about 375F from a second preheatzone or lift line 12 fed via line 13 with the flue gas having atemperature of about 1400F from the interstage incineratorrecuperator 24fed via line 16. In thefirst preheat zone 10, the oil shale is preheatedto about 200F while being transported to accumulator 17 and cycloneseparator 18 wherein oil shale particles are separated from flue gas.The partially preheated oil shale is then transferred by gravity feed tothe second preheat zone 12 via lines 19 and 20 at a rate of about 450tons per hour to be further preheated therein. The flue gas having atemperature of about 225F from cyclone separator 18 and containing oilshale dust and water is passed through a wet scrubber (not shown) andthen vented to the atmosphere at a low temperature of about F.Approximately 30 gallons per minute of water are removed from the shalein this first preheat zone 10 which do not have to be carried throughthe downstream preheating and retorting zones and ultimately removedfrom the oil product.

In the lift line or second preheat zone 12, the oil shale is furtherpreheated to about 350F while being transported by hot flue gas havingan entry temperature of about 800F. The hot flue gas in the secondpreheat zone 12 is fed thereto via line 21 and consists of the flue gasfrom the third preheat zone 22 having an exit gas temperature of about575F which is fed via line 23 to interstage incinerator-recuperator 24wherein it is reheated to a temperature of about 1400F by the combustionof hydrocarbons evolved during the final preheat operation, oil shalefines, and supplementary fuel. The 1400F flue gas is cooled in a heatrecovery zone 24 d to about 800F before it enters the second preheatzone 12. The shale is separated from the flue gas in accumulator 25 andcyclone separator 26 and fed via lines 27 and 28 to the third preheatzone 22. Some additional water vapor is removed in the second preheatzone 12.

The partially preheated oil shale at about 350F is introduced into thethird preheat zone 22 wherein it is contacted and transported by fluegas introduced at about 1200F to about 1400F vialine 29 so as touniformly preheat the entire raw shale stream to about 550F withouteffecting significant pyrolysis thereof prior to the retorting inpyrolyzer 30. The flue gas to the final preheat zone 22 comprises ablend of the ball heater flue gas fed via line 15 which may be cooled ifnecessary for process control purposes by adding quench air at about100F to 120F via line 31. The preheated oil shale is separated from theflue gas in accumulator 32 and cyclone separator 33 and thereafter fedto the retort via lines 34 and 35 wherein the pyrolysis of the oil shaleis effected by contact with hot ceramic bodies fed from the ball heater14 via line 36.

The incinerator-recuperator 24 generally comprises a combustion zone 24a in which air and fuel are burned, a mixing zone 24 b in which the fluegas from line 23 is mixed with combustion products from zone 24 a, anincineration zone 24 0 wherein the oil shale fines and hydrocarbons fromthe third preheat stage 22 are incinerated, and a heat recovery zone 24d for cooling the flue gas to about 800F prior to exiting via line 21.The heat recovery zone 24 d may incorporate conventional air heatexchangers and/or waste heat boilers for steam generation.

in the ball heater 14, ceramic balls are introduced from ball elevator37 via line 38 into the heating chamber 39 wherein the balls arecontacted with hot flue gas from a combustion chamber 40. Air and fuelare supplied via lines 41 and 42, respectively, to an atomizing typeburner (not shown) located in the combustion chamber wherein the mixtureis burned to provide hot flue gas. As the ceramic balls and flue gas arecocurrently drawn downward through the ball heater, the balls are heatedwhile the flue gas is cooled. The hot flue gas is withdrawn from theball heater 14 via disengaging zone 43 and line 44 for use in the rawshale preheat zone 22. The heated balls are withdrawn from ball heatingzone 39 via line 36 and fed to pyrolyzer 30.

In the rotating pyrolysis drum 30, the hot ceramic balls from the ballheater 14 are contacted with the raw shale preheated to about 550F toeffect the pyrolysis thereof. The balls and oil shale pass co-currentlythrough the pyrolyzer 30 where the heat of the balls is imparted to theoil shale with the production of an effluent hydrocarbonaceous shale oilvapor and processed shale solids. The effluent vapor, processed shalesolids and cooled balls exit from pyrolysis drum 30 through tunnel 45and pass to a rotating trommel screen 46 having openings therein suchthat the comminuted processed shale solids pass through while thepassage of the large size balls is precluded. The effluent vapor isremoved from vapor dome 47 and passed via line 48 to a recovery section(not shown). Substantially all the processed shale solids pass throughtrommel screen 46 and into processed shale solids accumulator 49 fromwhich they are removed via line 50 and passed to a processed shalesolids disposal area. Cooled balls are removed from accumulator 51 bymeans of line 52,

6 passed to ball elevator 37 and returned to the ball heater 14 via line38 to be reheated therein.

In the above description of the preferred embodiment, the temperaturesof the various flue gas and solid streams are exemplary of one set ofpreheat conditions that have been found to be desirable when processinga specific type and grade of oil shale. These conditions have been foundapplicable to oil shale from the Mahogany Zone of the Piceance Basinlocated in northwestern Colorado. Mahogany Zone oil shale usuallycontains 30 to 40 gallons of recoverable liquid hydrocarbons per ton ofore processed. If either lower or higher grades of oil shale areprocessed, the flue gas and solids temperatures in each of therespective lift lines may have to be altered in order to optimize thesystem. Thus, when preliminary tests on a particular grade of oil shaleindicate that it is desirable to either increase or decrease the degreeof preheat in any one of the three stages of preheat for the purpose ofaltering atmospheric hydrocarbon emissions and/or fuel supply to thepreheat zone, the preheat conditions may be altered without departingfrom the basic concept herein disclosed.

Tests have been performed at a plant capable of processing 1000 tons perday of Mahogany Zone oil shale to determine the amount of hydrocarbonsgenerated under specified preheat conditions for each of the threestages of preheat. From these tests, it has been determined that inpreheating oil shale (crushed to minus /2- inch) from 50F to 500F in athreestage system, an average of 400 to 700 ppm of hydrocarbons isgenerated. Of this amount, 400 to 500 ppm of hydrocarbons are generatedin the final stage of preheat, and to ppm of hydrocarbons are generatedin the first two stages. In these tests, the lift lines were operated atflue gas inlet temperatures of approximately 500F, 900F and 1000F,respectively, while the shale was heated to successively highertemperatures of approximately 200F, 350F, and 500F, respectively, ineach of the three stages of preheat.

Another series of tests was performed to determine the conditionsrequired to substantially reduce the hydrocarbon content of the flue gasdischarged from the third lift line, and the approximate particle sizeand organic carbon content of the oil shale fines entrained in the fluegas. Table 2 presents an average particle size analysis of oil shalefines which entered the incineration zone from the third preheat stage.

TABLE 2 Particle Size Analysis of Oil Shale Fines Entering IncinerationZone Table 3 presents analyses of the organic carbon content of oilshale fines which were obtained from isokinetic samples taken at theinlet and outlet of the combustion chamber while operating anincineration zone at temperatures in the range of from 1330F to I425 F.

These data illustrate that the fines contain organic carbon which can beburned to recover its heating value.

TABLE 3 Organic Carbon Content of Entrained Oil Shale Fines Fines FinesOrganic Combustion Organic as Carbon Content, lb/hr Chamber Carbon of(Based on 450 TPH Sample Location wt Feed Shale Feed) Inlet 16.05 0.36536 Outlet 0.23 8

Inlet 5.91 0.39 214 Outlet 0.10 4

TABLE 4 Hydrocarbon Reduction with Incineration Zone Between Second andThird Preheat Stages Hydrocarbon Incineration Zone Samples IncinerationResidence Inlet Outlet Zone Temp. Time HC I-IC Efficiency F Sec ppm ppm1220 0.31 2129 475 71.2 1260 0.29 2129 346 79.3 1275 0.39 9l3 47 93.21290 0.4! 1021 12 98.4 1325 0.48 75l 9 98.5 1330 0.47 1040 11 98.6 13450.48 648 3 99.4 1350 0.33 1214 9 99.0 I355 0.32 1632 17 98.6 1360 0.50890 12 98.2 1375 0.4l 3846 2 99.9 1385 0.55 986 II 98.4 1390 0.49 ll9 299.7 I420 0.50 508 3 99.2 1425 0.52 1230 6 99.4 1435 0.52 1226 7 99.71440 0.53 I005 4 99.5

From the above three tables, it is evident that a significant amount ofvery fine oil shale is entrained in the flue gas stream which can beused as a source of fuel for the preheat system that would otherwise notbe recovered. In addition, it is apparent from Table 4 that theinterposition of an incineration zone between the second and thirdpreheat stages is very effective in reducing=the hydrocarbon content ofthe flue gas when the incineration zone is operated at a temperature inexcess of about 1300F, and preferable at about 1400F, at residence timesin the order of at least 0.5 seconds.

From the above description of the improved process of the invention, itwill be apparent that the process provides a procedure for retorting orpyrolyzing oil shale which utilizes the whole shale, including the finematerial, to recover substantially 100% of the recoverable hydrocarbonseither as a liquid and gaseous product or as fuel in the preheat system.Moreover, the process provides for the preheating of raw oil shale totemperatures in the order of 400F to 650F without significantlyeffecting pyrolysis of a major portion of the shale 8 prior to theretorting or pyrolysis operation. Furthermore, the process providesincreased heat economy by discharging low temperature, rather than hightemperature, flue gas to the atmosphere.

The process, in addition, provides for substantial elimination ofhydrocarbon emissions by combusting hydrocarbon vapors that are derivedprimarily by vaporization of bitumen contained in the shale. The use ofa single preheat lift line to obtain these higher preheat temperaturesis not practical because the fresh raw shale would be contacted by hightemperature flue gases, i.e., l200F to 1400F which would result insevere hydrocarbon emissions. In addition, if a single preheat lift linewere operated in the manner just described, the flue gas dischargetemperature would necessarily be in the order of 600F, and wouldobviously contain substantial amounts of unburned hydrocarbons.

It will be appreciated that various modifications and changes may bemade in the process of the invention by those skilled in the art withoutdeparting from the essence thereof. Therefore, the invention is to belimited only within the scope of the appended claims.

What is claimed is:

1. A process for preheating oil shale to a temperature in the order of400F to 650F prior to the pyrolysis thereof in a retort which comprisesheating the oil shale in a series of at least two dilute phase fluidizedbeds by entraining partially preheated oil shale in the final dilutephase fluidized bed with hot flue gas to provide oil shale preheated tobetween about 400F and 650F for introduction into the retort andpartially cooled flue gas containing entrained oil shale fines andhydrocarbon vapors, passing the partially cooled flue gas through anincineration zone and incinerating in the presence of combustionproducts the entrained oil shale fines and hydrocarbon vapors emanatingfrom the final dilute phase fluidized bed to provide a portion of thefuel requirement to reheat the flue gas, cooling the flue gas from theincineration zone and entraining crushed raw oil shale in a first dilutephase fluidized bed with the cooled flue gas from the incineration zoneto provide partially preheated oil shale for subsequent introductioninto the final dilute phase fluidized bed and cooled flue gas.

2. The process as defined in claim 1 wherein the entrained oil shalefines and hydrocarbon vapors are incinerated at a temperature in excessof about l300F.

3. The process as defined in claim 2 wherein the residence time of theentrained oil shale fines and hydrocarbon vapors in the incinerationzone is between about 0.3 second and 1.0 second.

4. The process as defined in claim 1 wherein the flue gas from theincineration zone is cooled to a temperature below about 900F.

5. The process as defined in claim 1 comprising the further step ofentraining partially preheated oil shale from the first dilute phasefluidized bed in a second dilute phase fluidized bed with the cooledflue gas from the incineration zone to provide partially preheated oilshale for subsequent introduction into the final dilute phase fluidizedbed and partially cooled flue gas for introduction into the first dilutephase fluidized bed.

6. The proces as defined in claim 5 comprising the further steps ofpassing the partially cooled flue gas from the second dilute phasefluidized bed through a second incineration zone so as to partiallyreheat the flue gas and combust entrained hydrocarbon vapors and oilshale fines emanating from the dilute phase fluheated to a temperatureof about 350F. idized beds downstream of the first dilute phase fluid-8. The process as defined in claim 1 wherein the resiized bed prior tocooling and introducing the partially dence time of the flue gas in theincineration zone is bereheated flue gas into the first dilute phasefluidized 5 tween about 0.5 second and 1.0 second at an incinerabed.tion zone temperature of between about 1400F and 7. The process asdefined in claim 1 wherein the oil about l500F. shale feed to the finaldilute phase fluidized bed is prea

1. A PROCESS FOR PREHEATING OIL SHALE TO A TEMPERATURE IN THE ORDER OF400*F TO 650*F PRIOR TO THE PYROLKYSIS THEREOF IN A RETORT WHICHCOMPRISES HEATING THE OIL SHALE IN A SERIES OF AT LAST TWO DILUTE PHASEFLUIDIZED BEDS BY ENTRAINING PARTIALLY PREHEATED OIL SHALE IIN THE FINALDILUTE PHASE FLUIDIZED BED WITH KHOT FLUE GAS TO PROVIDE OIL SHALEPREHEATED TO BETWEEN ABOUT 400*F AND 650*F FOR INTRODUCTION INTO THERETORT AND PARTIALLY COOLED FLUE GAS CONTAINING ENTRAINED OIL SHALEFINES AND HYDROCARBON VAPORS, PASSING THE PATIALLY COOLED FLUE GASTHROUGH AN INCINERATION ZONE AND INCINERATING IN THE PRESENCE OFCOMBUSTION PRODUCTS THE ENTRAINED OIL SHALE FINES AND HYDROCARBON VAPORSEMANATING FROM THE FINAL DILUTE PHASE FLLUIDIZED BED TO PROVIDE APORTION OF THE FUEL REQUIREMENT TO REHEAT THE FLUE GAS, COOLING THE FLUEGAS FROM THE INCINERATION ZONE AND ENTRAINING CRUSHED RAW OIL SHALE IN AFIRST DILUTE PHASE FLUIDIZED BED WITH THE COOLED FLUE GAS FROM THEINCINERATION ZONE TO PROVIDE PARTIALY PREHEATED OIL SHALE FOR SBSEQUENTINTRODUCTION INTO THE FINAL DILUTE PHASE FLUIDIZED BED AND COOLED FLUEGAS.
 2. The process as defined in claim 1 wherein the entrained oilshale fines and hydrocarbon vapors are incinErated at a temperature inexcess of about 1300*F.
 3. The process as defined in claim 2 wherein theresidence time of the entrained oil shale fines and hydrocarbon vaporsin the incineration zone is between about 0.3 second and 1.0 second. 4.The process as defined in claim 1 wherein the flue gas from theincineration zone is cooled to a temperature below about 900*F.
 5. Theprocess as defined in claim 1 comprising the further step of entrainingpartially preheated oil shale from the first dilute phase fluidized bedin a second dilute phase fluidized bed with the cooled flue gas from theincineration zone to provide partially preheated oil shale forsubsequent introduction into the final dilute phase fluidized bed andpartially cooled flue gas for introduction into the first dilute phasefluidized bed.
 6. The proces as defined in claim 5 comprising thefurther steps of passing the partially cooled flue gas from the seconddilute phase fluidized bed through a second incineration zone so as topartially reheat the flue gas and combust entrained hydrocarbon vaporsand oil shale fines emanating from the dilute phase fluidized bedsdownstream of the first dilute phase fluidized bed prior to cooling andintroducing the partially reheated flue gas into the first dilute phasefluidized bed.
 7. The process as defined in claim 1 wherein the oilshale feed to the final dilute phase fluidized bed is preheated to atemperature of about 350*F.
 8. The process as defined in claim 1 whereinthe residence time of the flue gas in the incineration zone is betweenabout 0.5 second and 1.0 second at an incineration zone temperature ofbetween about 1400*F and about 1500*F.